This invention relates to post-type fuse holders and more particularly to fuse holders in which the side terminal is assembled from the exterior of the barrel of the fuse holder and the connection between the side terminal and fuse carrier is disposed interior of the barrel without unduly exposing the side terminal to the interior of the barrel.
A post-type fuse holder is a device for retaining an electrical fuse in a wired circuit. A standard post-type fuse holder is comprised of a barrel, a cap, and means for electrically connecting the fuse holder and fuse, which the fuse holder retains, to an electrical circuit. Commonly, the means for connecting the fuse holder to a circuit is a male terminal which is sized to fit standard female wiring terminals. The fuse holder operates by electrically insulating the fuse from the environment exterior the fuse holder while creating an electrically conductive circuit from one terminal, through the fuse holder and fuse, to the second terminal The fuse holder is typically constructed into cap and barrel sections, and incorporates some means for disassembly to facilitate removal and replacement of the fuses.
Two types of cylindrical fuses are commonly used to fuse circuits to which this invention applies. The first type is the American-style fuse, which is a cylinder approximately 1/4 of an inch in diameter and 11/4 inches in length. The other is the European-style fuse, which is approximately 5 mm in diameter and 20 mm in length. Fuse holders are commonly constructed to hold both types of fuses, although the European-style is both shorter and slimmer than the American-style fuse.
One type of fuse holder known in the prior art has a fuse holding barrel which retains one end of a fuse and two electrical wiring access terminals, and a cap which retains the other end of the fuse and completes the electric path between the two electrical access terminals when the cap is inserted in the barrel. To facilitate the contact with the fuse, the bottom terminal is connected to the base of the barrel with a protrusion projecting interior the barrel, and the side terminal is placed interior the barrel and has a protrusion which projects through the wall of the barrel for wiring access. The cap contains an integral conductor which both physically and conductively engages the fuse, and which upon assembly of the cap and fuse within the barrel completes an electric circuit by conductively engaging the side terminal inside the barrel. To reduce the risk of shock and arcing which could occur when the fuse holder cap is removed, and to meet safety standards, an insulating sleeve or spacer-sleeve is disposed interior the barrel between the fuse and the barrel wall, such that only the portion of the side terminal substantially in contact with the cap conductor is exposed to the interior of the barrel. Thus, this type prior art fuse holder, disposing the side terminal within the fuse holder, requires an internal spacer-sleeve to insure that the fuse holder is shock proof, i.e., that the internal exposed live metal is not accessible to the user when holding the fuse carrier with the fuse installed or with the standard I.E.C. test finger. When the spacer sleeve is used, the sleeve must first be assembled to the side terminal, and then the subassembly must be guided blindly into a receiving aperture inside the fuse holder barrel. Where the side terminal is exposed to the interior bore of the barrel, a foreign object inserted into the barrel can make electrical contact with the side terminal
U.S. Pat. No. 4,448,476 describes a type of fuse holder which does not use the insulating sleeve. Rather, the bottom and side terminals are molded into the body of the barrel such that only the contact points of the bottom and side terminals are exposed interior the barrel This reduces the risk of shock or arcing when a fuse is inserted or removed from the fuse holder.
U.S. Pat. No. 3,891,292 also discloses a fuse holder having side and bottom terminals with an insulating sleeve located within an interior tubular contact. The side terminal is located within the barrel in this construction by placement from within the barrel through an aperture located in an undercut on the exterior of the body. Electrical contact from the side terminal to the fuse is maintained through a tubular contact and through a conductive spring to a fuse. A circular lip in the interior of the barrel isolates the side terminal from the interior of the barrel, and an insulating sleeve disposed interior the tubular contact electrically isolates the tubular contact from the interior of the fuse holder.
Some prior art fuse holders have a side terminal which is assembled from the outside of the fuse holder, but their point of electrical contact to the fuse carrier is also exposed on the outside of the assembled fuse holder. Such an assembly makes the connection between the side terminal and fuse carrier susceptible to contamination from foreign particles, corrosion, or damage during handling or assembly Other prior art fuse holders have a side terminal which is assembled from the outside of the fuse holder, but do not have a cap which is substantially fully retained within the fuse holder barrel, and the point of making electrical contact is outside the barrel or the assembly requires the use of a sleeve.
Another problem associated with post-type fuse holders is stress relieving which occurs in the metal components therein. This is a particular problem with the cap portion of the fuse holder, which holds a metal fuse carrier inside which must grip the fuse when the cap is removed from the fuse holder barrel. Typically, the fuse carrier includes a tangentially inward projecting flap which serves the dual function of retaining a spring within the cap to bias the fuse against the bottom terminal and grip the end cap of the fuse. During the removal of the fuse from the fuse holder barrel, the friction between the flap and fuse end cap caused by the spring force tending to restrain the outward force of the end cap against the flap holds the fuse in the end cap. However, during the life of the fuse holder, heat cycling caused by the heating of the fuse during short term circuit overloads causes stress relieving in the flap, thereby reducing the spring pressure holding the fuse in the fuse carrier. Thus, it is not uncommon in older fuse holders for the fuse to remain in the fuse holder after the cap and fuse carrier are removed. As a result, the user of the fuse holder must remove the fuse by hand, which could result in a shock to the user.